In Phase I the focus in the laboratory of Dr. Robert Schwartz will be the immunology of the AKR mouse, specifically as it relates to the development of thymic lymphoma/leukemia. In the planned research the candidate will be exposed to a range of methodologies in immunology and will further develop his skills in the design and critical evaluation of scientific experiments. In cooperation with the laboratory of Dr. John Coffin, the candidate will utilize immunologic tools and molecular biologic methods in a strategy to characterize the receptor by which the recombinant polytropic retrovirus of AKR mice enters cells. Phase II is envisioned to extend the studies of the retroviral receptor. Using reagents developed during Phase I the applicant will focus on the biology of the polytropic virus receptor as it relates to transformation in the AKR mouse and investigate the physiologic role of this cell surface component. It is anticipated that Phase II will be conducted with the continued input and support of the co-sponsors, however the candidate will proceed more independently so that the transition to a fully independent investigator will readily be achieved by grants end.